Method and apparatus for forming an article and an article formed thereby

ABSTRACT

A method for forming an article in which thermoplastics materials are used as the binding agent. Materials ( 21 ) are shredded in a shredder ( 1 ), compressed in a compressing chamber ( 15 ) and moulded in a moulding chamber ( 16, 17, 19, 20, 26, 27 ). The thermoplastics material is heated whilst the material is held under compression and then cooled to bind the material together. In one embodiment superheated steam is supplied via tubes ( 31 ) having apertures there along. In another embodiment superheated steam is supplied via apertures in side walls of the mould ( 58, 59 ). Blocks ( 62, 72 ) formed by the method and apparatus of the invention may find application as construction materials etc. and have good structural, thermal and acoustic properties.

FIELD OF THE INVENTION

[0001] The present invention relates to a method and apparatus forforming an article in which thermoplastics materials are used as thebinding agent. The invention also relates to an article formed by themethod or apparatus.

BACKGROUND OF THE INVENTION

[0002] A major challenge facing developed nations is dealing with thevolumes of waste produced. Efforts have been made, in particular, inrelation to the recycling of plastics and paper waste. Approaches to therecycling of plastics have focused upon processes where plastics aresorted into the various types and controlled proportions are utilised toproduce recycled products.

[0003] A report entitled “Assessing the potential for post-use plasticswaste recycling—predicting recovery in 2001 and 2006” produced by theAssociation of Plastics Manufacturers in Europe identified the mainconstraints for improving recycling rates for plastic as:

[0004] i/ the imbalance between the waste collectable and the potentialend-markets for the recycled plastics

[0005] ii/ the presence of large quantities of mixed plastics wastewhere the difficulties and energy consumed in separating into homogenousfractions and cleaning outweigh the environmental gain of mechanicalrecycling.

[0006] The report considered there to be an upper limit to potentialdemand for mechanically recycled plastics. This report reflects thecommon mind set of those in the industry that tightly control sorting isrequired to produce a valuable product. It also reflects the commonlyheld perception that there is a limited marked for the types of articlesthat may be produced.

[0007] In the report “SIRA International (1999). Australian PlasticsMaterials Recycling Survey—Report for Plastics and Chemicals IndustriesAssociation. Canberra, Australia” the major problems facing recyclarswere identified as:

[0008] Separation of difficult plastics

[0009] Contamination between polymers

[0010] Contaminated waste

[0011] Plastics re-processing is highly labour intensive for low returns

[0012] Demand is unbalanced with supply

[0013] Not enough end users

[0014] Collection and separation

[0015] Plastic recyclers currently recycle plastics into seven types asfollows:

[0016] Code 1: Polyethylene Terephthalate (PET or PETE)

[0017] Code 2: High Density Polyethylene (HOPE)

[0018] Code 3: Vinyl (Polyvinyl Chloride or PVC)

[0019] Code 4: Low Density Polyethylene (LOPE)

[0020] Code 5; Polypropylene (PP)

[0021] Code 6: Polystyrene (PS)

[0022] Code 7; Other

[0023] Tightly controlled sorting is expensive and is a significant costcomponent in current recycling processes. Where tightly controlledsorting has been required it has been difficult to produce a marketableproduct economically. The characteristics of many products produced insuch recycling processes have been considered to be inferior.

[0024] There has also been a prejudice against the use of polyethylenefilm in recycling processes. In “Siegler, T. & Perkins, R. (1999).Sorting Plastic Bottles for Recycling. Ascotney, Vermont: DSMEnvironmental Services for The American Plastics Council” the followingpoints were noted:

[0025] “Acceptance of even small amounts of recyclables in plastic bagswill significantly reduce equipment efficiency unless all of the film isremoved with a film removal system at the front end.”and

[0026] “The composition of material delivered to the MRF (materialsrecovery facility) has a significant impact on processing efficiency.Contaminants entering MRFs 5, 6, and 7 represented between 3.7% and 6.7%of the incoming material. This seemingly small amount of incomingcontamination was responsible for between 31 and 67% of sorting labourat these the MRFs.”and

[0027] “Increased public education is necessary to better informparticipating households which plastic containers are acceptable in therecycling program.”

[0028] Rathje, W and Murphy, C. cite as one of the “Five Major Mythsabout Garbage and Why They're Wrong” that:

[0029] “The biggest problem faced by recycling is not the technologicalprocess of turning one thing into another. Anything can be recycled—andwould be if demand for what it could be recycled into were great enough.The key, then, is demand, and demand for many recyclables is oftensoft.”

[0030] To date the most commercially attractive recycling progresseshave been those utilising industrial waste. Industrial waste maytypically consist of large batches of one type of plastics which avoidsthe need for any sorting process.

OBJECT AND STATEMENT OF THE INVENTION

[0031] It is an object of the present invention to provide a method andapparatus for forming an article from mixed plastics waste whichovercomes these problems or at least provides the public with the usefulchoice.

[0032] According to a first aspect to the invention there is thusprovided a method of forming an article comprising the steps of:

[0033] i/ introducing into a chamber material to be formed containing asufficient amount of thermoplastics material to bind the materialtogether;

[0034] ii/ compressing the material within the chamber so that itoccupies a reduced volume;

[0035] iii/ generating sufficient steam within the chamber to meltsufficient thermoplastics material substantially throughout the materialto bind the material together when cooled; and

[0036] iv/ releasing an article produced from the chamber.

[0037] The energy source may be superheated steam, a microwave energysource or en ultrasonic energy source. The material is preferably amixture of shredded thermoplastics and other materials. The material ispreferably compressed in a first direction and then in a seconddirection transverse to the first direction. The material may be furthercompressed in a third direction transverse to the first and seconddirections. The article formed may either be cooled within the chamberby liquid or air or released into a cooling medium.

[0038] According to a further aspect to the invention there is provideda method of forming an article comprising the steps of:

[0039] i/ introducing into a chamber material to be formed containing asufficient amount of thermoplastics material to bind the materialtogether when cooled;

[0040] ii/ compressing the material within the chamber so that itoccupies a reduced volume;

[0041] iii/ introducing sufficient superheated steam into the receptacleto melt sufficient thermoplastics material to bind the material togethersubstantially throughout the material; and

[0042] iv/ releasing an article produced from the chamber.

[0043] The material is preferably compressed in a first direction andthen in a second direction transverse to the first direction. Thematerial may be further compressed in the third direction transverse tothe first and second directions.

[0044] The material is preferably a mixture of shredded thermoplasticsand other materials. Superheated steam is preferably introduced into thechamber either by apertures in one or more side of the chamber or viatubes inserted into the chamber when steam is introduced. Thetemperature of the superheated steam is preferably between 200° C. to400° C., more preferably 260° C. to 320° C., most preferably 280° C. to300° C. The pressure maintained within a chamber is preferably between 5to 100 psi, more preferably 5 to 60 psi, most preferably 10 to 20 psi.Superheated steam is preferably introduced into the mould for a periodof between 10 seconds to 6 minutes, preferably 10 to 60 seconds, mostpreferably 10 to 20 seconds. Where the temperature is hold constant atabout 300° C. and supplied for a period of about 15 seconds the pressuremaintained within a chamber is preferably between 5 to 26 psi, morepreferably 5 to 20 psi, most preferably 10 to 15 psi. Where thetemperature of the superheated steam is about 300° C. and the pressureis maintained at about 15 psi the superheated steam is preferablysupplied for a period of between 10 to 16 seconds. The material ispreferably reduced in volume by factor of between 5:1 to 25:1, morepreferably by factor of between 10:1 to 20:1. The material may includeup to 20% non-thermoplastic material, preferably up to 10%non-thermoplastic material.

[0045] According to a further aspect to the invention there is providedan article forming apparatus including:

[0046] a moulding chamber for receiving and containing compressedmaterial including thermoplastics material; and

[0047] outlets for providing superheated steam into the chamberpositioned to provide sufficient heat substantially throughout thematerial within the chamber to melt the thermoplastics substantiallythroughout the material.

[0048] The outlets may be in the form of apertures in one or more faceof the moulding chamber or in the form of one or more tube havingapertures for providing a relatively even distribution of superheatedsteam throughout the chamber. The apparatus may include a compressingchamber for compressing the material prior to moulding. One pair ofwalls may move together in a first direction, a second pair of walls maymove together in a second direction, transverse to the first direction,and a third pair of walls may move together in a third directiontransverse to the first and second directions. The moulding chamber ispreferably defined by the first, second and third pairs of walls whenmoved together.

[0049] According to a further aspect to the invention there is providedan article forming apparatus including:

[0050] a compressing chamber for receiving material and compressing itin at least two transverse directions to a reduced volume; a mouldingchamber for containing the compressed material; and

[0051] a microwave source for supplying microwave radiationsubstantially throughout the moulding chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The invention will now be described by the way of example withreference to the accompanying drawings in which:

[0053]FIG. 1: is a schematic diagram of an article forming systemaccording to a first embodiment to the invention.

[0054]FIG. 2: is a cross sectional side view of the article formingapparatus with material to be formed loaded in the compression chamber.

[0055]FIG. 3: shows a cross sectional side view of the article formingapparatus after a first stage of compaction.

[0056]FIG. 4: shows a front cross sectional view of the article formingapparatus.

[0057]FIG. 5: shows a front cross sectional view of the article formingapparatus after a second stage of compression.

[0058]FIG. 6: shows a front cross sectional view of the apparatus aftera third stage of compression has been performed.

[0059]FIG. 7: shows a front cross sectional view of the apparatus whensteam injection tubes have been inserted into the moulding chamber.

[0060]FIG. 8: shows a side cross sectional view of the article formingapparatus as shown in FIG. 7.

[0061]FIG. 9: shows a side cross sectional view of the article formingapparatus after a moulded article has been ejected.

[0062]FIG. 10: shoes a front cross sectional view of the apparatus asshown in FIG. 9.

[0063]FIG. 11: shows the hydraulic circuit for the system of FIGS. 1 to10.

[0064] FIGS. 11A and B: show front and side cross sectional views of thehydraulic circuit of the article forming apparatus.

[0065]FIG. 12: shows a schematic diagram of a water circuit for thesystem of FIGS. 1 to 11.

[0066]FIG. 13: shows a front cross sectional view of an article formingapparatus according to a second embodiment.

[0067]FIG. 14: shows a side cross sectional view of the article formingapparatus of FIG. 13.

[0068]FIG. 15: shows a front cross sectional view of an article formingapparatus according to a third embodiment.

[0069]FIG. 11: shows a side cross sectional view of the article formingapparatus of FIG. 16.

[0070]FIG. 17: shows an article in the form of a block produced by anyone of the article forming apparatus of FIGS. 1 to 16.

[0071]FIG. 18: shows a wail constructed of blocks of the type shown inFIG. 17.

[0072]FIG. 19: Shows a cross sectional view of a wall formed using theblocks of FIG. 17.

[0073]FIG. 20: Shows a cross sectional view of a wall formed using theblocks of FIG. 17 when threaded onto a road.

[0074]FIG. 21: Shows a cross sectional view of a wall formed using theblocks of FIG. 17 when threaded onto a post.

[0075]FIG. 22: Shows a cross sectional view of a wall formed using theblocks of FIG. 17 with irrigation means provided.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0076] Referring firstly to FIG. 1 a schematic diagram of a system forforming an article according to a first embodiment will be described.Material to be processed is supplied to shredder 1. The materialprovided to shredder 1 includes a sufficient proportion of thermoplasticmaterial to bind the article together when processed. Preferably, thematerial is waste plastic material. Mixed waste plastic material may beprovided in a substantially unsorted state. Sorting into plastics typeswill generally not be required for normal mixtures of domestic waste.Some sorting may be desirable to exclude undesirable non plasticsmaterials included within the waste such as large non-plastic items orexpanded polystyrene. Preferably greater than 80% and more preferablygreater than 90% of the material consists of plastics material.

[0077] Shredder 1 preferably shreds the material into strips. A suitableshredder is a PT 45 shredder produced by Peak Technology Limited ofWellington New Zealand. The material is preferably shredded into stripsof between 10 to 20 mm in width, most preferably about 16 mm in width.There will be a certain degree of variation in strip width due to theshredding process and a certain degree of roughness of the edge of theshredded material may be advantageous as discussed later.

[0078] As well as plastics materials certain other materials such assawdust, wood chip, paper or other fibres may be added up to an amountof about 20% although preferably less than 10%.

[0079] The shredded material is fed by feed-hopper 2 into a washing anddrying drum 3. An auger 5 is provided along the length of the drum tofeed material through the drum as it is rotated. In first stage 4 wateris sprayed upon the shredded material as it passes through the firststage and auger 5 advances the material through the drum to a perforateddrying section 6. In a second rinse stage 7 the shredded material isagain sprayed with hot water and auger 5 advances the shredded materialthrough section 7 into drying section 8. Prying section 8 has largeperforations which allow water to drain from the shredded material.Residual heat retained by the material after being heated by the hotrinse water facilitates drying of the material. The entire drum 3 isrotated via an hydraulic or an electric motor.

[0080] Shredded material from drying section 8 is fed to accumulator 9and fad by auger or conveyor 10 to article forming apparatus 11. Boller12 provides steam to superheater 13 which provides superheated steam toarticle forming apparatus 11.

[0081] Referring now to FIG. 2 a side cross sectional view of an articleforming apparatus according to a first embodiment is shown. Afeed-hopper 14 supplies shredded material to a compressing chamber 15.Compressing chamber 15 consists of three pairs of walls that may bemoved together to compress the material therein. A first pair of walls16 and 17 are shown in FIG. 2. Wall 17 is fixed in this case and wallmay 16 may be moved towards wall 17 upon extension of ram 18. Once ram18 is extended wall 16 moves to the position shown in FIG. 3.

[0082] Referring now to FIG. 4 a front cross sectional view of apparatus11 is shown. In this view side walls 19 and 20 are seen to containshredded material 21 there between after walls 16 and 17 have been movedtogether in a second stage of compression rams 22 to 25 are extended tomove walls 19 and 20 to the position shown in FIG. 5. As shown in FIG. 5the shredded material 21 has undergone compression in a first directionand then a second direction transverse to the first direction. Movingtwo wails together in the second compressing stage assists in eveningthe stock of compressed material.

[0083] In a third stage of compression walls 26 and 27 are movedtogether. Rams 28 and 29 are extended to move walls 26 and 27 togetherto the position shown in FIG. 6. The material has then undergonecompression in a third direction transverse to the first and seconddirections of the prior compression stages.

[0084] Compressing the shredded material in one direction and at least afurther direction transverse to the first direction is considered to beadvantageous. Compressing the material in a single direction can resultin alignment of strips. Compressing the material in transverse directionassists in producing a structure that is less aligned in any singledirection. This process also assists in promoting interlocking of therough edges of strips of material to assist in binding the materialtogether. However, in some applications alignment of the strips could bedesirable in which case compression in single direction could be used.The compressing chamber is preferably vertically elongate to minimisethe footprint of the apparatus and to promote even distribution ofmaterial 21 (i.e. avoid peaking of material in the stack). Compressionis preferably substantially equal in each stage (about 2.5:1 in eachstage). Different densities of block may be formed by filling thecompressing chamber with different weights of material.

[0085] After the three stages of compression the three pairs of wells 16and 17, 19 end 20 and 25 and 27 have moved together to define a mouldingchamber containing shredded material 21. Although in this embodiment themoulding chamber is formed as part of the compressing chamber it will beappreciated that a separate moulding chamber and compressing chamber maybe employed.

[0086] In the next step of the process sufficient energy must beprovided to the moulding chamber to melt sufficient thermoplasticsmaterial within shredded material 21 so that, upon cooling, the materialwill be substantially bound together. Material 21 is saturated with heatenergy to ensure a relatively consistent bonded matrix is formed.Polyethylene is a large component of typical domestic waste and hasexcellent adhesive properties as utilised in hot glue guns. Low densitypolyethylene is usually a difficult waste for recyclers to deal with andconstitutes a large proportion of residential waste. Polyethylene may bemelted front a crystalline form and upon cooling returns to acrystalline form. It is an effective binding agent in the method of theinvention. Other low melting point thermoplastics may also be utilisedto bind the material together.

[0087] In order to achieve an economic process producing a viableproduct, a sufficient amount of energy to melt the bindingthermoplastics material substantially throughout the article must beprovided within a relatively short time period. According to a firstaspect to the invention superheated steam is introduced via tubes havingapertures along their length so as to achieve heating of thethermoplastic material throughout the mould to provide effectivebinding.

[0088] Referring now to FIG. 7 the moulding stage according to the firstaspect to the invention will be described. In FIG. 7 there is shown amanifold 30 having a plurality of tubes 31 extending therefrom. In thisexample tubes 31 have an outside diameter of 9.5 mm and a wall thicknessof between 0.9 to 1.2 mm. 2 mm apertures are drilled through the tube at25 mm spacings and the end of the tube is closed to form a pointed end.Superheated steam is input to manifold 30 via inlet 32 and output intotubes 31. Tubes 31 are distributed throughout the chamber duringmoulding and are provided with apertures at intervals along their lengthto provide superheated steam at a variety of locations throughout themoulding chamber. As shown in FIG. 7 ram 33 extends to insert tubes 31through apertures in wall 26 into material 21. The moulding chamber issubstantially sealed and the pressure within a chamber can be controlledvia an adjustable relief valve 34. In this example the chamber isdimensioned to form a block of approximately 200 mm by 200 mm by 400 mm.Steam is introduced at a prescribed temperature and pressure for apredetermined period to ensure that the correct amount of energy issupplied to the material 21 at an appropriate rate.

[0089] The superheated steam preferably has a temperature within themanifold 30 of between 200° C. to 400° C., more preferably 260° C. to320° C., most preferably 280° C. to 300° C. The pressure maintainedwithin the moulding chamber is preferably between 5 to 100 psi, morepreferably 5 to 60 psi and most preferably 10 to 20 psi. The period ofsupply of superheated steam to the moulding chamber is preferably to 10sac to 5 min, more preferably 10 to 60 sec. most preferably 10 to 20sec.

[0090] The objective is to provide sufficient heat throughout the mouldto melt sufficient thermoplastics materials to effectively bindmaterials 21 together on cooling. The heat must be applied at anappropriate temperature and pressure to avoid degradation of the productand to make the process economic. Operating parameters will varydepending upon the materials concerned and the density of product to beformed. Certain preferred operating parameters have been determined formixed waste plastics as follows.

[0091] One approach is to maintain temperature and period of supply ofsuperheated steam substantially constant and to vary the pressuremaintained within the moulding chamber. It has been found experimentallythat good quality products can be achieved when the temperature of thesuperheated steam is maintained at about 300° C. and supplied for aperiod of about 15 sec. For a high density block (275 to 350 kg/m⁸) thepressure is preferably maintained at between 15 to 25 psi. For mediumdensity block (200 to 270 kg/m³) the pressure is preferably maintainedat between to 20 psi. For a low density product (between 100 to 200kg/ma³) the pressure is preferably maintained at between 5 to 15 psi.Different densities of block may be desirable for different applicationssuch as structural blocks, acoustic blocks, thermal insulation etc. Amanifold temperature of about 300° C. is advantageous as it is lowenough not to degrade the material but high enough to deliver energysufficiently quickly. This temperature is easily and economicallyachieved with a superheater. This temperature also allows the pressureto be kept relatively low. Use of a fixed cycle time means that priorand subsequent process steps are not affected by the type of articlebeing produced.

[0092] Another approach is to maintain the temperature of thesuperheated steam constant at about 300° C. and the pressure constant atabout 15 psi. In this case the period of supply of steam to the mouldingchamber will typically vary between 10 to 20 sec. This will depend uponthe materials utilised.

[0093] Referring again to FIG. 7 it will seen that venting is providedvia variable pressure relief valve 34 at the top of the mould. It ispreferable to provide venting at the top of the mould as the energydistribution from tubes 31 tends to have a pear shape distributiontowards the bottom of the mould. By venting at the top, steam from thebottom travels through the top zone and results in more uniform heatingof all materials in the block.

[0094] Once sufficient steam has been supplied to the moulding chambermanifold 30 and tubes 31 are retracted by ram 33. After a sufficientquantity of superheated steam has been supplied to a mould cooling wateris introduced Via inlet 35. Any suitable cooling liquid or gas may beutilised although water is preferred. Cooling the article 21 formed inthe mould has the advantage of fixing the article in the shape of themould prior to ejecting it. However, article 21 may be ejected from themould into a cooling fluid.

[0095] Upon cooling of article 21 wall 27 may be rotated by ram 36 toallow a formed block 21 to be ejected from the moulding chamber as shownin FIGS. 9 and 10.

[0096] Referring now to FIG. 11 an hydraulic circuit for the system ofFIGS. 1 to 10 is shown. An hydraulic tank 37 supplies hydraulic fluid toan hydraulic power source 38. This supplies hydraulic fluid to drivehydraulic motor 39 which rotates drum 3 Hydraulic power source 38 alsoprovide hydraulic fluid to drive hydraulic motor 41 of conveyor 10.Hydraulic fluid is also supplied from power source 38 to shredder motor42. Hydraulic fluid is returned via return lines (dashed lines) tohydraulic tank 37. Hydraulic power source 38 also provides pressurisedhydraulic fluid to hydraulic controller 40 which supplies fluid to therams of apparatus 11 under the control of programmable logic controller(PLC) 43,

[0097]FIGS. 11A and 11B show the hydraulic circuit from hydrauliccontroller 40 to rams 18, 22 to 25, 28 and 29, 33 and 36. These arecontrolled to operate in the appropriate sequence by PLC 43.

[0098] Referring now to FIG. 12 a water circuit for the system of FIGS.1 to 11B is shown. Clean water is supplied to water tank 44 whichsupplies water to hotwell tank 46. Hot water from hotwell tank 45 issupplied to washing tank 46. Washing tank 46 supplies hot water tosprayer 47 for the first wash of shredded material. Hot water for thesecond rinse is supplied from hotwell tank 45 to sprayer 48. Excesswater from the two drying stages is collected in drip trays 49 and 50,is filtered by filters 51 and 52 and pumped by pump 53 back to washingtank 46. Although filtered, the water in washing tank will be of a lowerquality than the other tanks and is suitable for the first wash cycle.

[0099] Water from hotwell tank 45 is also supplied to boiler 54. Boiler54 supplies steam to superheater 55. Superheater 55 supplies superheatedsteam to three way valve 56 which supplies superheated steam to manifold30 of apparatus 11 or to condenser 57 to be returned to hotwell tank 45.Cooling water to cool a moulded article is supplied to inlet 35 fromhotwell tank 45. Water collected from drip tray 58 is returned tohotwell tank 45.

[0100] Referring now to FIGS. 13 and 14 an apparatus according to asecond aspect of the invention is shown. In this case a relatively thinarticle is to be formed and superheated steam is supplied via side wallsof the moulding chamber. The article forming apparatus is identical tothe apparatus described above except that top wall 26 and manifold 30are replaced by mould portion 58 and wall 27 is replaced by wall 59. Inthis case superheated steam is supplied via inlet 60 to an interiorcavity of mould portion 58. Superheated steam from the interior cavityof mould portion 58 passes through a number of apertures adjacent thesurface of mould portion 68 opposite material 21. Likewise, wall 59 hasa cavity therein and apertures are provided in the face of wall 69adjacent material 21 and are distributed so as to provide relativelyuniform heating throughout material 21. This method is suitable whererelatively thin articles are to be manufactured. Apart from theprovision of steam via apertures rather than tubes operation is as perthe embodiment shown in FIGS. 1 to 12,

[0101] Referring now to FIGS. 15 and 16 a further alternative embodimentis shown which again is identical to apparatus 11 except that manifold30 and needles 31 have been replaced by a microwave transmitter 61. Inthis case heating energy is supplied to wet material 21 by microwaveradiation rather than through the use of superheated steam. In this caseit is necessary to supply water to the moulding chamber and for thechamber to be sealed so that elevated pressures can be achieved. Watermay be injected into the mould or wet material may be introduced. Themicrowave radiation heats the water to form superheated steam throughoutthe moulding chamber. Operation is otherwise identical to that describedabove. Other energy sources that can heat moisture throughout themoulding chamber may also be employed.

[0102] Referring now to FIG. 17 an article in the form of a block formedby the apparatus of the invention is shown. In this case block 62 hasrecesses 63 formed in the one face and corresponding protrusions 64formed an opposite face. The protrusions 64 may be engaged withincorresponding recesses 63 of adjacent blocks when forming a wall asshown in FIG. 18 the protrusions 64 end recesses 63 help to locateblocks and maintain lateral stability. A block may of course be producednot having projections or recesses.

[0103] Referring now to FIGS. 19 to 22 interengaging projections andrecesses are not shown, although they could be employed, in the wallsshown in FIG. 19 the wall is built upon a concrete foundation 71 formedon ground 70. Blocks 72 are stacked one on top of the other and securedtogether via any suitable adhesive. The blocks may be secured togetherutilising an adhesive product, such as a bitumastic material which curesin the atmosphere or glue from a hot glue gun.

[0104] In this embodiment the blocks are coated with nutrient and orpropagation material such as seeds. Further, an irrigation tube 74 maybe provided along the top to irrigate the plants growing on the wall.

[0105] The blocks 72 may preferably include a certain amount of paper orother material suitable to retain moisture which provide a suitablemedium for the material propagate thereon. Recycled plastics materialmay provide a suitable porous structure into which the roots of plantsmay extend to form a natural self supporting structure.

[0106] Referring now to FIG. 20 an alternative embodiment is shown inwhich a rod 75 preferably formed of steel, extending from a concretefooting 76 is secured in ground 77. A plurality of blocks 72 havelongitudinal bores provided therethrough so that blocks 72 may bethreaded along a series of poles 75 provided at intervals. The bores inblocks 72 may be formed in an offset manner so that the blocks may beoffset between layers.

[0107]FIG. 21 shows a similar embodiment in which a wooden post 78extends from a concrete foundation 79 and a plurality of blocks 72 arethreaded on post 78 through apertures formed therein.

[0108]FIG. 22 shows a wall similar in construction to that shown in FIG.20 in which bracelines 80 are utillised to stabilise the wall. Thebracelines 80 may either extend adjacent blocks 72 or may taper awayfrom the blocks towards the base as shown in the two configurations.Buttresses may also be provided at intervals along any of the abovewalls to provide additional stability.

[0109] It will thus be seen that the present invention provides a methodand apparatus for producing articles from plastic waste materialsuitable for use in construction, insulation, acoustic barriers etc. Themethod of the invention enables substantially unsorted plastics waste tobe processed into viable construction materials. The use of mixedplastics materials without sorting provides significant economies overprior methods. The apparatus of the invention is relatively simple andcan be constructed at relatively low cost. The method of the inventionallows building materials to be produced economically from plasticswaste.

[0110] Products formed by the method of the invention have good shockresistance and absorption characteristics making them suitable for usein structures prone to earthquakes or vibration. Products formed by themethod of the invention also have good thermal insulation and acousticisolation properties making them suitable for use in certain buildingapplications. The material also has memory and so can return back to itsoriginal shape after deformation.

[0111] The present invention is seen as a significant advance in theprocessing of mixed waste plastics by eliminating the need for sortingplastics into individual plastic types.

1. A method of forming an article comprising the steps of: i/ introducing into a chamber material to be formed containing a sufficient amount of thermoplastics material to bind the material together; ii/ compressing the material within the chamber so that it occupies a reduced volume; iii/ generating sufficient steam within the chamber to melt sufficient thermoplastics material substantially throughout the material to bind the material together when cooled; and iv/ releasing an article produced from the chamber.
 2. A method as claimed in claim 1 wherein the material is compressed in one direction and then in a second direction transverse to the first direction.
 3. A method as claimed in claim 2 wherein the material is subsequently compressed in a third direction transverse to the first and second directions.
 4. A method as claimed in any one of the preceding claims wherein superheated steam is supplied to the chamber from a superheated steam source.
 5. A method as claimed in claim 4 wherein the superheated steam is supplied through one or more side wall of the chamber.
 6. A method as claimed in claim 4 wherein the superheated steam is supplied via tubes supplied with superheated steam having apertures along their length which are inserted into the chamber in step
 111. 7. A method as claimed in any one of claims 1 to a wherein fluid within the chamber is heated by a microwave energy source to generate steam.
 8. A method as claimed in claim 7 wherein water is injected into the chamber before microwave energy is supplied.
 9. A method as claimed in any one of the preceding claims wherein the material is shredded prior to being placed within the chamber.
 10. A method as claimed in claim 9 where the material is shredded into strips of about 10 to 20 mm in width.
 11. A method as claimed in claim 9 or 10 wherein the strips have rough edges.
 12. A method as claimed in any one of claims 9 to 11 wherein the material is washed and dried after being shredded and before being placed within the chamber.
 13. A method as claimed in any one of the preceding claims wherein the thermoplastics material is waste plastics.
 14. A method as claimed in claim 13 wherein the thermoplastics material is a mixture of different types of waste plastics.
 15. A method as claimed in claim 13 wherein the thermoplastics material includes PETE and/or polyethylene.
 16. A method as claimed in any one of claims 13 to 15 wherein the other material to be formed includes at least one of sawdust, wood chips, fibres and paper.
 17. A method as claimed in any one of the preceding claims wherein the article is cooled by introducing liquid to the chamber prior to release of the article in step iv.
 18. A method as claimed in any one of the preceding claims where the article is cooled by introducing air to the chamber prior to release of the article in step iv.
 19. A method as claimed in any one of claims 1 to 16 wherein the article is cooled by releasing it from the chamber into a fluid bath.
 20. A method of forming an article comprising the steps of: i/ introducing into a chamber material to be formed containing a sufficient amount of thermoplastic material to bin the material together; ii/ compressing the material within the chamber to that it occupies a reduced volume; iii/ introducing sufficient superheated steam into the chamber to melt sufficient thermoplastics material substantially throughout the material to bind the material together when cooled; and iv/ releasing an article produced from the chamber
 21. A method as claimed in claim 20 wherein the material is compressed in one direction and then in a second direction transverse to the first direction.
 22. A method as claimed in claim 21 wherein the material is subsequently compressed in a third direction transverse to the first and second directions.
 23. A method as claimed in any one of claims 20 to 22 wherein the material is shredded prior to being supplied to the chamber.
 24. A method as claimed in claim 23 wherein the material is shredded into strips of about 10 to 20 mm in width.
 25. A method as claimed in claim 24 wherein the strips are shredded so as to have rough edges which interlock when compressed.
 26. A method as claimed in any one of claims 23 to 25 wherein the shredded material is washed and dried prior to being supplied to the chamber.
 27. A method as claimed in any one of claims 20 to 26 wherein the thermoplastics material is waste plastics.
 28. A method as claimed in claim 27 wherein the thermoplastics material is a mixture of different types of waste plastics.
 29. A method as claimed in claim 27 or 28 wherein the thermoplastics material includes PETE and/or polyethylene.
 30. A method as claimed in any one of claims 27 to 29 wherein the material to be formed includes at least one of sawdust, wood chip, fibre and paper.
 31. A method es claimed in any one of claims 20 to 29 wherein the article is cooled by supplying cooling fluid to the chamber prior to releasing the article from the chamber.
 32. A method as claimed in any one of claims 20 to 30 wherein the article is cooled by introducing air into the chamber prior to releasing the article from the chamber.
 33. A method as claimed in any one of claims 20 to 30 wherein the article is cooled by releasing it from the chamber into a fluid bath.
 34. A method as claimed in any one of claims 20 to 33 wherein the superheated steam is supplied to the chamber via openings provided in one or more side well of the chamber.
 35. A method as claimed in any one of claims 20 to 33 wherein the superheated steam is supplied by inserting tubes into the chamber having apertures along their length for delivering superheated steam into the chamber at locations such as to ensure sufficient thermoplastics materials is melted throughout the article to bind the article together when it cools.
 36. A method as claimed in any one of claims 20 to 35 wherein superheated steam at a temperature between 200° C. to 400° C. is supplied to the chamber in step iii.
 37. A method as claimed in claim 36 wherein the superheated steam is at a temperature of between 260° C. to 320° C.
 38. A method as claimed in claim 36 wherein the superheated steam is at a temperature between 280° C. to 300° C.
 39. A method as claimed in any one of the preceding claims wherein a pressure of between 5 psi to 100 psi is maintained within the chamber during step iii.
 40. A method as claimed in claim 39 where the pressure is maintained at between 5 to 60 psi.
 41. A method as claimed in claim 39 when the pressure is maintained at between 10 to 20 psi.
 42. A method as claimed in any one of claims 20 to 41 wherein superheated steam is supplied into the chamber in step iii for a period of between 10 seconds to 5 minutes.
 43. A method as claimed in claim 42 wherein the period a between 10 to 60 seconds.
 44. A method as claimed in claim 42 wherein the period is between 10 to 20 seconds.
 45. A method as claimed in any one of claims 20 to 35 wherein superheated steam at a temperature of between 260° C. to 320° C. is supplied to the chamber for a period of between 10 to 20 seconds at a pressure of between 5 to 25 psi.
 46. A method as claimed in any one of claims 20 to 35 wherein superheated steam at a temperature of about 300° C. is supplied to the chamber for a period of about 15 seconds at a pressure of between 5 to 26 psi.
 47. A method as claimed in any one of claims 20 to 35 wherein superheated steam at a temperature of about 300° C. is supplied into the chamber for a period of between 10 to 15 seconds and a pressure of about 15 psi is maintained in the chamber.
 48. A method as claimed in any one of the preceding claims wherein the material is reduced in volume by a factor of between 5:1 to 25:1.
 49. A method as claimed in claim 48 wherein the material is reduced in volume by a factor of between 10:1 to 20:1.
 50. A method as claimed in any one of the preceding claims wherein the material includes up to 20% of material that is not thermoplastic material.
 51. A method as claimed in any one of the preceding claims wherein the material includes up to 10% of material that is not thermoplastic material.
 52. A method as claimed in claim 3 or claim 22 wherein the material is compressed by substantially the same amount in each direction of compression.
 53. An article formed by the method of any one of the preceding claims.
 54. An article as claimed in claim 53 wherein the article is in the form of a block
 55. An article as claimed in claim 54 wherein projections are provided on one face of the block and recesses are provided on an opposite face of the block wherein the projections and recesses are positioned to assist in correct location and interlocking of blocks when constructing a wall.
 56. An article as claimed in any one of claims 53 to 55 wherein apertures are provided through the block to receive reinforcing or aligning elements.
 57. An article as claimed in any one of claims 53 to 56 wherein nutrients and/or propagation material are applied to the article.
 58. An article forming apparatus including: a moulding chamber for receiving and containing compressed material including thermoplastics material; and outlets for providing superheated steam into the chamber positioned to provide sufficient heat substantially throughout the material within the chamber to melt the thermoplastics material substantially throughout the material.
 59. An apparatus as claimed in claim 58 wherein the outlets are in the form of apertures provided in one or more face of the moulding chamber.
 60. An apparatus as claimed in claim 58 wherein the outlets are in the form of one or more tube having apertures at spaced intervals which are introduced into the chamber when the material is supplied to the chamber and retracted prior to the removal of the material from the moulding chamber.
 61. An apparatus as claimed in claim 60 wherein a plurality of tubes provide superheated steam to the chamber.
 62. An apparatus as claimed in claim 61 wherein the tubes are fed from a common manifold and the tubes and manifold are moved in unison with respect to the moulding chamber.
 63. An apparatus as claimed in any one of claims 58 to 62 wherein the moulding chamber is substantially sealed and is provided with a pressure relief mechanism.
 64. An apparatus as claimed in claim 63 wherein the pressure release mechanism is adjustable.
 65. An apparatus as claimed in any one of claims 58 to 64 including a compressing chamber for compressing the material for supply to the moulding chamber wherein one or more pairs of walls of the compressing chamber may be moved together to compress material therein.
 66. An apparatus as claimed in claim 65 wherein the compressing chamber is vertically elongate.
 67. An apparatus as claimed in claim 66 or claim 66 wherein one pair of walls of the compressing chamber are moved together to compress the material in a first direction and a second pair of walls of the chamber are moved together in a second direction transverse to the first direction to compress the material in a second direction.
 68. An apparatus as claimed in claim 67 wherein one wall of the one pair of walls is stationary and the other is movable relative thereto.
 69. An apparatus as claimed in claim 67 or claim 68 wherein both walls of the second pair of walls move together to compress the material.
 70. An apparatus as claimed in any one of claim 67 to 69 wherein the first and second directions both lie in a substantially horizontal plane.
 71. An apparatus as claimed in any one of claims 67 to 70 wherein a third pair of walls may be moved together in a third direction transverse to the first and second directions to provide a third stage of compression.
 72. An apparatus as claimed in any one of claims 67 to 71 wherein the pairs of walls are driven by hydraulic rams.
 73. An apparatus as claimed in claim 71 wherein the moulding chamber is defined when the first, second and third pairs of walls have been moved together to compress the material therein.
 74. An apparatus as claimed in claim 73 wherein a flap is provided in the lower of the third pair of walls which may be opened to release a moulded article.
 75. An apparatus as claimed in any one of claim 58 to 74 including a fluid supply valve for supplying cooling fluid to the moulding chamber.
 76. An article forming apparatus including: a compressing chamber for receiving material and compressing it in at least two transverse directions to a reduced volume; a moulding chamber for containing the compressed material; and a microwave source for supplying microwave radiation substantially throughout the moulding chamber.
 77. An apparatus as claimed un claim 76 wherein the moulding chamber is substantially sealed and is provided with a pressure relief mechanism.
 78. An apparatus as claimed in claim 77 wherein the pressure release mechanism is adjustable.
 79. An apparatus as claimed in any one of claims 76 to 78 including a compression chamber for compressing the material for supply to the moulding chamber wherein one or more pairs of walls of the compressing chamber may be moved together to compress material therein.
 80. An apparatus as claimed in claim 79 wherein the compressing chamber is vertically elongate.
 81. An apparatus as claimed in claim 79 or claim 80 wherein a first pair of walls of the chamber may be moved together to compress the material in a first direction and a second pair of walls of the chamber may be moved together in a second direction transverse to the first direction to compress the material in a second direction.
 82. An apparatus as claimed in claim 81 wherein one wall of the first pair of walls is stationary and the other moves relative thereto.
 83. An apparatus as claimed in claim 81 or claim 82 wherein both walls of the second pair of walls move together to compress the material.
 84. An apparatus as claimed in any one of claims 81 to 83 wherein the first and second directions both lie in a substantially horizontal plane.
 85. An apparatus as claimed in any one of claims 81 to 84 wherein a third pair of walls may be moved together in a third direction transverse to the first and second directions to provide a third stage of compression.
 86. An apparatus as claimed in any one of claims 81 to 85 wherein the pairs of walls are driven by hydraulic rams.
 87. An apparatus as claimed in claim 85 wherein the moulding chamber is defined when the first, second and third pairs of walls have been moved together to compress the material therein.
 88. An apparatus as claimed in claim 87 wherein a flap is provided in the lower of the third pair of walls which may be opened to release a moulded article.
 89. An apparatus as claimed in any one of claims 76 to 88 including a fluid supply valve for supplying cooling fluid to the moulding chamber. 